1. Field of the Invention
The present invention relates generally to refractory pouring assemblies for pouring molten metal during a continuous casting process. More particularly, the invention relates to a refractory pour tube for use in such assemblies.
2. Description of Related Art
Refractory pouring assemblies for transferring melt, i.e., molten metal, are known in the art. For example, in a typical casting process, the melt is transferred from a ladle to a tundish, and from the tundish to a mold. The ladle and tundish each have a bottom wall with a port through which the melt exits. A valve assembly of some type is provided to control the flow of melt from the ladle to the tundish, and from the tundish to the mold. In order to transfer the melt from such bottom pouring metallurgical vessels, the valve assembly is provided with a refractory pour tube having upper and lower ends for receiving and discharging the melt.
One known valve assembly includes a plate fixed to the exterior surface of the bottom wall of the vessel, the plate having an opening aligned with the port in the vessel wall. A combined tube and plate assembly is secured beneath the fixed plate and is selectively alignable with the opening in the fixed plate. During a casting process, the valve is actuated to its open position and the melt exits the vessel through the opening in the plate and passes into the pour tube. See, for example, the pouring assemblies disclosed in U.S. Pat. Nos. 5,348,202, 5,198,126 and 4,746,037.
In conventional refractory pouring assemblies that include a combined pour tube and plate, the plate is formed of an abrasion resistant composition in order to protect the plate during relative sliding against a mating valve plate. Additionally, forming the plate of a hard, wear resistant composition ensures that the peripheral edge around the opening in the plate is hard enough to cut through a metal shell formed in the tube. The body portion of the tube, which is not subjected to sliding abrasion, typically is formed of a refractory composition that is softer and more resistant to thermal shock.
As is known in the art, aspiration of air through the pouring assembly should be avoided because it results in build up of alumina deposits that clog the pouring tube or adversely affect the quality of the cast metal. However, prior art pour tube and plate assemblies formed from separate refractory elements include joints between the elements. This is undesirable because air can be aspirated through the joints, resulting in the problems mentioned above. In one known pour tube construction, a separately formed flat plate of wear resistant refractory is attached to a pour tube by a metal can. This arrangement does not always prevent aspiration of air through the assembly due to the joint between the plate and the tube. Further, air gaps and separation of components can arise during use due to the different rates of thermal expansion of the various materials forming the plate and tube.
In another combined pour tube and plate construction, the plate and tube are co-pressed from different refractory compositions to form a one-piece composite member. While this construction is more likely to prevent air aspiration, than one in which separate elements are joined by a can, manufacturing the composite tube and plate is expensive and requires precise machining. A metal can typically is used with this construction as well and directly contacts the exterior of the combined pour tube and plate. The exterior of the tube and plate thus must be precisely machined to fit properly within the can. This increases the cost and difficulty associated with producing such a construction. Accordingly, there is a need in the art for a refractory pour tube that overcomes shortcomings of the prior art.